The present invention relates to the laser sensor art. It finds particular application when detecting objects at very short distances and will be described with particular reference thereto.
Laser sensors have a rather extensive variety of applications in many fields. They are used to provide an easily perturbable equilibrium, such as in a security system. They also gauge the location and orientation of moving objects, such as on an assembly line. They are also used to judge the distance from the sensor to a target. In general, laser sensors are useful when information about a remote object is desired, such as whether the object is present and, if so, its distance.
Heretofore, laser sensors have included a laser diode or other laser source which was focused to a preselected focal length by a convergent focusing lens. Laser light reflected from a reflector or reflective surface was received by another convergent lens with a relatively long focal length and focused on a photodiode detector. The output of the photodiode was monitored and an electronic signal was generated indicative of the reception of the reflected laser beam or the absence of the reflected laser beam. In order to distinguish between the reflected laser beam and stray light of like color, some laser sensors included a feedback system, such as a continuous wave type feedback system, between the laser source and the detector.
Although successful, such prior laser sensors have drawbacks. In general, the use of a convergent light beam requires one focal point to be set at the point of convergence. As a result, different focal lengths require different lenses. A design is desired that will allow different focal lengths without having to change between different lenses.
The present invention provides a new and improved laser method and apparatus that solves the above referenced problems and others.
In accordance with one aspect of the present invention, a laser is provided. A laser diode emits laser light. A collimating lens mounted adjacent the laser diode collimates the emitted laser light. Reflected laser light encounters a pivotable mirror whose angle selects a convergence distance. A photoreceiver receives reflected laser light from the adjustable mirror and produces an output signal indicative of the receipt/non-receipt of reflected laser light.
In accordance with another aspect of the present invention, a method of laser sensing is provided. Laser light is emitted and collimated into a collimated beam. The collimated beam is transmitted across a region and is reflected off a target object back across the region and reflected from an adjustable mirror, which mirror was adjusted to set a convergence distance. The laser light reflected from the adjustable mirror is detected. A presence/absence of reflected laser light is determined.
One advantage of the present invention is that it senses over ranges of about 5 to 50 cm.
Another advantage of the present invention is that no lens replacements are required to change between distance ranges. The same sensor can be used for all distances within the range of the apparatus without lens changes.
Another advantage is ease of alignment on small targets.
Another advantage resides in insensitivity to background objects beyond a point of convergence.
Yet another advantage of the present invention is that it provides extremely accurate spatial data.
Still further benefits and advantages of the present invention will become apparent to those of ordinary skill in the art upon reading and understanding the following detailed description of the preferred embodiments.